I actually thought about a Slender styled custom story back when Slender was fresh, and I imagined it would work quite well. The mechanics are similar, but HPL2 seems like a way more refined engine than what the original Slender was made in.

Nah, it's not really that difficult. Of course it depends on each person, but as far as scripting goes, I think this is easier than anything else I've tried (granted I haven't tried that many different engines though). It might take a little while to get into, but once you do, it will progress quite fast, subjectively speaking. Took me about 2 days to understand how to navigate the level editor, then 2 months later I had created something playable. I wouldn't say what I made was very good, but I think it was a good start, and people seemed to enjoy it. Of course you pick up more and more knowledge as you work with it. Even today I learn new stuff, and I've worked with HPL2 for 1.5 years so far.

Just remember, you don't need to know everything about it to use it. Like half of the features are optional. You can come very far with just your creativity.

I recommend to start with the poor ones (teleporting naked guys, no story, bugs on mass, Pewdiepie dedicated) and then start increasing the quality. Because if you start with custom stories like "The Great Work", "White Night", "Obscurity" you will be disappointed with the shitty ones.

Play some beginner storied first, thats how i started it too
Naked guys, undetailed levels would be good. But they are damn boring. And most of them are related to famous crappy youtubers. I hate this cry guy so much... other beginner stories are full of pony stuff. So think about choosing a short but interesting project

The question that will never be answered:SOMA WHY ARE YOU SO BEAUTIFUL? ;_;

That was just me being unrealistic and sarcastic..
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Just a "Makes_no_sense" reply
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Anyway,
IF this guy really want to play some more story''s.
I would recommend what MasterPig said.
Start with the more ugly ones.
Then proceed to the better ones and then to the ones who has the best gameplay \ story \ atmosphere Etc..
The best mods are mostly longer mods and can be Full Conversion mods.
For further questions about what NOT to play and what are MUST play story's we can help you with that, even tho i guess thre might be a subtreath for this? not 100% sure tho.
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Good luck with the first bad ones, and enjoy the bigger great mods!